Schedule

Winter 2017

Active galactic nuclei are highly variable objects. To study the variability on time scales from minutes to years and understand the underlying emission processes, continuous long-term monitoring is crucial. The First G-APD Cherenkov Telescope (FACT) is a small imaging air Cherenkov telescope observing at TeV energies. It is pioneering the use of solid state photosensors (SiPM aka G-APDs) in ground-based gamma-ray astronomy. To get an unbiased data sample, a small set of sources is observed as much as possible. The presentation will give an introduction to the instrument and discuss how the use of SiPMs and the automatic operation, minimize the gaps in the light curves and maximize the duty cycle of the instrument. Results from more than five years of monitoring will be summarized including flaring activities of the blazars Mrk 421, Mrk 501 and 1ES 1959+650.

Fall 2015

Date

Time

Speaker

Title

Description

Friday October 9

1pm

Henrike Fleischhack, DESY

Towards a measurement of the iron spectrum in cosmic rays with VERITAS

Measuring the element-dependent energy spectra of cosmic rays plays an important role in understanding their acceleration and propagation. Most current results are obtained either from direct measurements by balloon- or satellite-borne detectors, or from indirect measurements by air shower detector arrays on the Earth’s surface. Imaging Atmospheric Cherenkov Telescopes (IACTs), used primarily for γ-ray astronomy, can also be used for cosmic-ray physics. They are able to measure Cherenkov light emitted both by heavy nuclei and by secondary particles produced in air showers, and are thus sensitive to the charge and energy of cosmic ray particles with energies of tens to hundreds of TeV.

In this talk, a likelihood method will be presented which improves the reconstruction of iron-induced air showers, as well as the suppression of backgrounds from lighter elements.

Summer 2015

Date

Time

Speaker

Title

Description

Friday July 10

1pm

Jordon Myslik, University of Victoria in Canada

Neutrino Oscillations at T2K

Since first being proposed to explain a dramatic difference between theoretical expectations and experimental observations, neutrinos have managed to maintain their mysterious reputation. The phenomenon of neutrino oscillation, where a neutrino of one flavor is observed to have changed into another while in transit, has been an area of intense experimental scrutiny. The T2K ("Tokai to Kamioka") experiment is a long-baseline neutrino oscillation experiment in Japan. A beam of muon neutrinos or muon antineutrinos is produced at the Japan Proton Accelerator Research Complex (J-PARC) in Tokai. The unoscillated neutrino flux is measured by the near detector complex 280 m from the proton target, and the oscillated neutrino flux is measured by the far detector, Super-Kamiokande, 295 km away. Using a beam of muon neutrinos, T2K has performed precise measurements of muon neutrino disappearance, and discovered muon neutrino to electron neutrino oscillation by measuring electron neutrino appearance. Since the summer of 2014, T2K has been taking data using a beam of muon antineutrinos, and has recently released its first result using antineutrino beam mode data: a muon antineutrino disappearance measurement. This talk will discuss these neutrino oscillation results, and using the recent muon antineutrino disappearance measurement as an example, give an overview of what goes into a T2K neutrino oscillation measurement.

Thursday June 4

1pm

Dr. Antonia Hubbard, U. of Wisconsin

First data from the DM-Ice17 Experiment at the South Pole

DM-Ice is a NaI(Tl) experiment searching for an annually-modulating dark matter signal. The DM-Ice17 detector has successfully operated in the South Pole ice for three years, and R&D efforts for the full-scale detector are underway at FNAL and the Boulby Underground Laboratory. I will present an analysis of the muon background in DM-Ice, including long-lived phosphorescence observed in both DM-Ice17 and DM-Ice37. The DM-Ice17 muon analysis also includes events that are coincident with IceCube. The expected annual modulation in the rate of muons is observed. The successful deployment and operation of DM-Ice17 establishes the South Pole ice as a viable location for future underground, low-background experiments in the Southern Hemisphere.

Winter 2015

Date

Time

Speaker

Title

Description

Tuesday Mar. 24th

1pm

Kerston Perez, Haverford College and Columbia University

Antideuteron Signatures of Dark Matter with the GAPS Experiment

The question of the origin of dark matter, the mysterious matter known to permeate the universe, is one of the towering problems of 21st-century physics. Dozens of dark matter search experiments are currently planned or ongoing, but these efforts have been hampered by the large background rates from conventional astrophysical processes and the vast array of signatures that could indicate a dark matter interaction. The General Antiparticle Spectrometer (GAPS) experiment aims to advance these searches by detecting low-energy antideuterons that result from the self-annihilation of dark matter particles in the Galactic halo, providing an essentially background-free signature of dark matter. This signal probes supersymmetry, extra-dimensional theories, and other modes dark matter production, complementing and extending the reach of current experiments. In this seminar, I will present the design and discovery potential of the baloon-borne GAPS experiment, which exploits a novel detection technique utilizing exotic atom capture and decay. In particular, I will detail the fabrication of the lithium-drifted Silicon detectors that are essential to its success.

Friday Mar. 13th

1pm

Daniel Whiteson, UC Irving

Observing Ultra-High Energy Cosmic Rays with Smartphones

We propose a novel approach for observing cosmic rays at ultra-high energy ($>10^{18}$~eV) by repurposing the existing network of smartphones as a ground detector array. Extensive air showers generated by cosmic rays produce muons and high-energy photons, which can be detected by the CMOS sensors of smartphone cameras. The small size and low efficiency of each sensor is compensated by the large number of active phones. We show that if user adoption targets are met, such a network will have significant observing power at the highest energies.

Friday Feb. 27th

1pm

Marcos Santander, Columbia University

Searching for the sources of cosmic-rays with VERITAS and IceCube

A century of cosmic-ray research has unveiled many of the key properties of these energetic particles that reach Earth from outer space. The sources of cosmic-rays, however, remain unknown. A potential clue to finding these elusive objects is the recent observation of an astrophysical flux of high-energy neutrinos by the IceCube detector as these particles may be produced in hadronic interactions near cosmic-ray accelerators. While the neutrino sky map shows no indication of point sources so far, their presence could be revealed by detecting the hadronic gamma-ray counterpart to the neutrino emission using the VERITAS air Cherenkov array. In this talk, I will describe the VERITAS and IceCube detectors, discuss the astrophysical implications of the neutrino flux observed by IceCube and outline how observations with gamma-ray telescopes can be used to reveal its origin.

Over 180 different molecular species have been detected in the Interstellar Medium. Although many of the molecules form in the gas-phase, there are some that are formed on surfaces of dust grains. Among these, molecular hydrogen and water are perhaps the most important ones because of their role in astrophysics (star formation) and astrochemistry/astrobiology. In the last decade, advances in observations via space telescopes and in laboratory techniques have led to great progress in characterizing the Molecular Universe. After an introduction about molecules and dust in the Interstellar Medium, I’ll present examples of how laboratory work and theoretical simulations have enabled us to understand how molecules form on stardust and how they influence the chemical evolution of the cosmos. Furthermore, I will show how specific knowledge acquired in the laboratory is guiding observations of actual processes in space.

Winter 2014

Date

Time

Speaker

Title

Description

Thursday Apr. 24th

1pm

Rachel Carr

The Double Chooz Experiment

The Double Chooz experiment, located in northeastern France, was designed to look for the oscillation of electron antineutrinos coming from nearby nuclear reactors. In 2011, it provided the first hint that this phenomenon exists, indicating that the neutrino mixing parameter theta_13 is nonzero. Since then, Double Chooz has developed many techniques to improve the precision of theta_13 measurements. I will talk about the experiment, our analyses, and what we've learned.

Thursday Mar. 27th

1pm

André Loose

Counting krypton atoms, one at a time

Atom trap trace analysis (ATTA) is a method to detect trace amounts of noble gas isotopes, with up to one part per quadrillion sensitivity - equivalent to one drop of water diluted into a water cube as tall as the Empire State Building. I will talk talk about the ATTA setup at Columbia, which will be used to monitor the krypton contamination in the XENON1T dark matter detector.

Thursday Feb. 27th

1pm

Mike Hahn

Evidence for Wave Heating in the Solar Corona

One of the major problems in astrophysics is to understand how the solar corona is heated to over a million degrees. In this talk I will review the coronal heating problem, its possible solutions, and present our results indicating that waves carry energy into the corona from lower layers of the Sun.

Tuesday Feb. 18th

1pm

Jose Alonso

Pushing the Envelope of Cyclotron Technology: from Medical Applications to Neutrino Sources

The Cyclotron, patented by E.O. Lawrence in 1934, has traditionally been a tool for nuclear physicists to study properties of nuclei. Even from the earliest days, however, applications of the beams from these machines in other fields have played an important role. Glenn Seaborg, in 1938 proposed the first use of an iodine isotope he discovered at the 27” cyclotron as a medical tracer, and in that same year Ernest's brother John Lawrence developed a program of treating tumors with neutrons from cyclotron beams hitting beryllium targets. Today cyclotrons are in widespread use: for radioisotope production, for cancer therapy with proton beams, and for increasingly-diversified programs in nuclear and particle physics research. This talk will cover the range of applications, and the evolution of machines optimized for each, and will explore new developments, from compact superconducting machines tailored for medical uses, up to and including a new project for development of very high-current cyclotrons as compact, cost-effective neutrino sources.

Thursday Jan. 30th

1pm

Tim Andeen

The ATLAS Experiment, from Nevis to CERN

Columbia University has a large team of scientists working on the ATLAS experiment at the Large Hadron Collider (LHC) at CERN in Geneva, Switzerland. Scientists from Nevis have been involved in every aspect of the experiment. Significant components of ATLAS were developed and built at Nevis and work continues upgrading the detector. The latest searches for physics beyond the Standard Model will be discussed as we look forward to even higher energy collisions in 2015 and beyond.

Fall 2013

Date

Time

Speaker

Title

Description

Dec. 17th

1pm

William Seligman

A Brief History of the Nevis Estate

Nov. 21st

1pm

Joy Didier

EBEX: The E and B EXperiment.

Measuring the polarization of the Cosmic Microwave Background (CMB) provides us with a wealth of information on the origin, composition and dynamics of the universe. EBEX is a balloone-borne telescope designed to measure the polarization of the CMB. I will give an overview of the instrument and of the recent science flight in Antarctica.

Oct. 24th

1pm

Ester Aliu

Astrophysics at the TeV scale

How experiments like VERITAS detect particles at this extreme energy and which scientific questions we try to address.The contribution of the Barnard and Columbia VERITAS groups will be described

Sept. 26th

1pm

Laboratories tour

Winter 2013

Date

Time

Speaker

Title

Description

Slides

May 9th

1:30 pm

Ken Miller

Laboratory Astrochemistry

From the early universe to the interstellar medium

Tues Apr. 16th

2:30 pm

Jose Alonso

Pushing the envelope of Cyclotron Technology: From Medical Applications to Neutrino Sources.

Mar. 28th

1pm

Andrew D. Harken

An overview of RARAF

From broad beams to microbeams, single proteins to small animals. Where we have been to where we are going.